BOS Checks

Voltage Tests. With the power on, safety gear donned, and all systems enabled, we checked for proper voltage with a multimeter on the battery bank (48 VDC) at the OutBack power center that’s interconnected with two PV systems and the grid (240 VAC), and both the DC and AC sides of the OutBack inverter. We also scrolled through the parameters programmed in the inverter to verify that they matched what was recorded in the MREA operation logs and that nothing had been changed.

Resistance testing. We then furled the machine and turned off the power from both the grid and the battery bank, since resistance checks cannot—and should not—be done while a system is energized. Still armed with a digital multimeter, now set to ohms, we checked the components in the controller box: fuses, a diode, a circuit breaker, a voltmeter, and an ammeter. The fuses and circuit breakers had continuity, the diode (electrical check-valve) was showing one-way conductivity, and the needles on the analog meters were free to move. The BOS components were verified to be in good working order and not the cause of Little Jake’s problems.

Wiring Checks

Conductor continuity & insulation testing. Next, we tested the underground wiring from the BOS to the junction box at the tower base. We disconnected both ends of the two wires (DC positive and negative) for continuity and insulation tests, using the multimeter to verify low resistance in the copper conductors and a megaohmeter or “megger” to test the THWN conductor insulation. Our megger was very old, with a hand crank and an analog display, but still accurate. Meggers are simple: The operator applies 500 or 1,000 volts to the conductors (in our case, with a hand crank), and the needle should display infinite resistance. Anything else signals insulation breakdown and/or a high-resistance fault. Our conductors passed both the continuity and insulation tests.

It was time to send a crew up the tower to test the wires from the junction box at the tower base to the slip-ring assembly near the tower top. (These were the same tests we just conducted from the BOS to the tower base.) We measured low resistance in the copper wires with a multimeter and saw infinite resistance with the megger. We also checked for short-circuits and insulation breakdown by connecting one test lead of the meter to the metal tower and the other test lead to each of the two power output conductors, one at a time. We were looking for infinite resistance from each conductor to the grounded tower on both the multimeter and the megger, and our tests confirmed that the wiring was good from the BOS to the top of the tower. This meant that our primary suspect was now the wind turbine itself.

Comments (1)

I was interested in the trouble-shooting approach.
It appears to have followed what we might call “the aardvark method”.
(“I am thinking of a word in the dictionary, what is it?”
“Is it aardvark?”
“No”
“Is it aardwolf?”
“No”
Etc.)
This method will eventually find a fault but it but it is not the fastest – and without due care has the potential to introduce more problems if (for example) connections are not done up again correctly.
Here in New Zealand I work for an appliance manufacturer (Fisher & Paykel Appliances Ltd.). In managing production engineering I have always been intrigued by various approaches to trouble shooting. We learned a great deal from the late Dorian Shainin when we had him here running some training sessions for us. (Look him up on the web is you are not familiar with him.) The technique he would propose for the dictionary would find any word with about 17 questions requiring just yes/no answers. (Find the middle page and ask if the word is before that page. Then go to the quarter or three-quarter point as appropriate. 11 questions will get you to the right page in a dictionary with up to 2048 pages. The next question gets you to the right column. Assuming there are no more than 32 words in a column, 5 more questions will get you to the right word.)
I recall one factory break-down where the photocell sensor was supposed to detect a cabinet on the assembly line, send a signal to a microprocessor controller, which in turn was supposed to drive a solid state relay which switched a hydraulic valve that operated a piston that did something useful. The problem was that when the cabinet went in front of the photocell the useful action didn’t happen. While I could have started by checking that the photocell was working, it was much quicker to repeatedly “cut the problem in half”. Because we had indicator lights across the electrical connections on hydraulic solenoids, (put there when the equipment was installed for just such trouble-shooting) the first check was to see if there was power getting to the solenoid when the photocell was triggered, etc. etc. (Without the indicator lights, the same thing could have been done with a meter – but when an assembly line is stopped, time is of the essence.).
You can bend the rules a bit if there is a very easy point to check that is not mid-way through the problem – or if there are other clues as to where to start looking.
I have learned that, if a piece of equipment has been operating OK and it stops, unless somebody has already had a go at trouble-shooting it by swapping components in and out before you arrive, it will very very rarely have more than one fault.
My objective, when called to an intractable malfunction, is to determine which component is faulty, get the tradesmen to replace it and walk away with confidence that the machine would work when they have done so.
While the mid-point of the Jacobs system in the article might be the input to the slip-rings, to save climbing the tower, checking first whether or not there was a voltage at the bottom would have isolated the problem to either the Balance of system and wiring to it from the tower or – to the generator, slip-rings and tower wiring. The next check at the generator terminals would have put the fault in the generator or in the slip rings and tower wiring etc.
(I’m not decrying checking such things as the brush and slip-ring condition while up the tower – but as maintenance tasks not as trouble-shooting in this case.)

Shainin, in my opinion was better (at least in this area) than either Joe Juran or Edward Deming – but not so well known, probably because he was better at solving problems than writing books.
I trust this might be useful.